diff --git a/src/formula.rs b/src/formula.rs
index b651fc4..f2700da 100644
--- a/src/formula.rs
+++ b/src/formula.rs
@@ -3,16 +3,21 @@ use crate::node::Node;
 #[derive(Clone)]
 pub struct Formula {
     tree: Node,
-    x: f64,
-    rating: f64,
 }
 
 impl Formula {
-    pub fn run(&mut self, inputs: Vec<f64>) -> Vec<f64> {
+    pub fn new() -> Self {
+        let mut formula = Self {
+            tree: Node::empty(),
+        };
+        formula.tree.modify_tree().add_node(Node::variable());
+
+        formula
+    }
+    pub fn run(&self, inputs: Vec<f64>) -> Vec<f64> {
         let mut outputs: Vec<f64> = vec![];
         for input in inputs {
-            self.x = input;
-            outputs.push(self.tree.get_value());
+            outputs.push(self.tree.get_value(input));
         }
         outputs
     }
diff --git a/src/main.rs b/src/main.rs
index e7a11a9..9e18c4f 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,9 @@
+use crate::formula::Formula;
+
+mod formula;
+mod node;
+
 fn main() {
-    println!("Hello, world!");
+    let formula = Formula::new();
+    dbg!(formula.run(vec![1f64]));
 }
diff --git a/src/node/handler.rs b/src/node/handler.rs
index 2612729..bebf744 100644
--- a/src/node/handler.rs
+++ b/src/node/handler.rs
@@ -2,17 +2,17 @@
 pub enum NodeHandler {
     Number { number: f64 },
     Function { function: fn(Vec<f64>) -> f64 },
-    Variable { getter: fn() -> f64 },
+    Variable,
     Empty,
 }
 
 impl NodeHandler {
-    pub fn run(&self, inputs: Vec<f64>) -> f64 {
+    pub fn run(&self, inputs: Vec<f64>, passed_x: f64) -> f64 {
         match self {
             NodeHandler::Number { number } => number.clone(),
             NodeHandler::Function { function } => function(inputs),
-            NodeHandler::Variable { getter } => getter(),
-            NodeHandler::Empty => 0f64,
+            NodeHandler::Variable => passed_x,
+            NodeHandler::Empty => inputs[0],
         }
     }
 }
diff --git a/src/node/mod.rs b/src/node/mod.rs
index 9288441..34dcad1 100644
--- a/src/node/mod.rs
+++ b/src/node/mod.rs
@@ -24,39 +24,46 @@ impl Node {
             max_children_count,
         }
     }
-    pub fn get_value(&self) -> f64 {
-        if self.children.len() == 0 {
-            return self.handler.run(vec![0f64]);
-        }
-        let mut inputs: Vec<f64> = vec![];
-        for node in &self.children {
-            inputs.push(node.get_value());
-        }
-
-        return self.handler.run(inputs);
-    }
-    pub fn modify_tree<'a>(&'a mut self) -> NodeModifier<'a> {
-        NodeModifier::from_random(self, None)
-    }
-    pub fn number(n: f64) -> Node {
-        Node {
+    pub fn empty() -> Self {
+        Self {
             children: vec![],
-            handler: NodeHandler::Number { number: n },
+            handler: NodeHandler::Empty,
             max_children_count: None,
         }
     }
-    pub fn function(func: fn(Vec<f64>) -> f64) -> Node {
-        Node {
+    pub fn number(n: f64) -> Self {
+        Self {
             children: vec![],
-            handler: NodeHandler::Function { function: func },
-            max_children_count: Some(1),
-        }
-    }
-    pub fn variable(getter: fn() -> f64) -> Node {
-        Node {
-            children: vec![],
-            handler: NodeHandler::Variable { getter },
+            handler: NodeHandler::Number { number: n },
             max_children_count: Some(0),
         }
     }
+    pub fn function(func: fn(Vec<f64>) -> f64, max_children_count: Option<usize>) -> Self {
+        Self {
+            children: vec![],
+            handler: NodeHandler::Function { function: func },
+            max_children_count,
+        }
+    }
+    pub fn variable() -> Self {
+        Self {
+            children: vec![],
+            handler: NodeHandler::Variable,
+            max_children_count: Some(0),
+        }
+    }
+    pub fn get_value(&self, passed_x: f64) -> f64 {
+        if self.children.len() == 0 {
+            return self.handler.run(vec![0f64], passed_x);
+        }
+        let mut inputs: Vec<f64> = vec![];
+        for node in &self.children {
+            inputs.push(node.get_value(passed_x));
+        }
+
+        return self.handler.run(inputs, passed_x);
+    }
+    pub fn modify_tree(&mut self) -> NodeModifier {
+        NodeModifier::from_random(self, None)
+    }
 }
diff --git a/src/node/node_modifier.rs b/src/node/node_modifier.rs
index ac2f932..b2cd066 100644
--- a/src/node/node_modifier.rs
+++ b/src/node/node_modifier.rs
@@ -4,6 +4,7 @@ use crate::node::functions;
 use rand::random_range;
 
 const PICK_STOP_PROBABILITY: u8 = 2;
+const TYPE_CHANGE_PROBABILITY: u8 = 10;
 
 pub enum NodeManipulationError {
     TooMuchChildren(Node),
@@ -11,14 +12,18 @@ pub enum NodeManipulationError {
 
 pub struct NodeModifier<'a> {
     picked_node: &'a mut Node,
-    function_mutation_pool: Vec<fn(Vec<f64>) -> f64>,
+    // This looks very monstrous, but it means "vector of functions for node paired with their maximum children count, if it exists"
+    function_mutation_pool: Vec<(fn(Vec<f64>) -> f64, Option<usize>)>,
     number_mutation_pool: Vec<fn(f64) -> f64>,
 }
 
 impl<'a> NodeModifier<'a> {
-    fn get_standard_pool() -> (Vec<fn(Vec<f64>) -> f64>, Vec<fn(f64) -> f64>) {
-        let standard_function_mutation: Vec<fn(Vec<f64>) -> f64> = vec![functions::sine];
-        // *4, /4, *2,
+    fn get_standard_pool() -> (
+        Vec<(fn(Vec<f64>) -> f64, Option<usize>)>,
+        Vec<fn(f64) -> f64>,
+    ) {
+        let standard_function_mutation: Vec<(fn(Vec<f64>) -> f64, Option<usize>)> =
+            vec![(functions::sine, Some(1))];
         let standard_number_mutation: Vec<fn(f64) -> f64> = vec![
             |x| x * 4f64,
             |x| x / 4.0f64,
@@ -32,8 +37,11 @@ impl<'a> NodeModifier<'a> {
     //Builders
     pub fn from_random(
         root: &'a mut Node,
-        custom_pools: Option<(Vec<fn(Vec<f64>) -> f64>, Vec<fn(f64) -> f64>)>,
-    ) -> NodeModifier<'a> {
+        custom_pools: Option<(
+            Vec<(fn(Vec<f64>) -> f64, Option<usize>)>,
+            Vec<fn(f64) -> f64>,
+        )>,
+    ) -> Self {
         let mut selected = root;
         while random_range(0..PICK_STOP_PROBABILITY) == PICK_STOP_PROBABILITY - 1 {
             let len = selected.children.len();
@@ -43,7 +51,7 @@ impl<'a> NodeModifier<'a> {
             selected = &mut selected.children[random_range(0..len)];
         }
         let pools = custom_pools.unwrap_or(NodeModifier::get_standard_pool());
-        NodeModifier {
+        Self {
             picked_node: selected,
             function_mutation_pool: pools.0,
             number_mutation_pool: pools.1,
@@ -51,10 +59,13 @@ impl<'a> NodeModifier<'a> {
     }
     pub fn from_node(
         node: &'a mut Node,
-        custom_pools: Option<(Vec<fn(Vec<f64>) -> f64>, Vec<fn(f64) -> f64>)>,
-    ) -> NodeModifier<'a> {
+        custom_pools: Option<(
+            Vec<(fn(Vec<f64>) -> f64, Option<usize>)>,
+            Vec<fn(f64) -> f64>,
+        )>,
+    ) -> Self {
         let pools = custom_pools.unwrap_or(NodeModifier::get_standard_pool());
-        NodeModifier {
+        Self {
             picked_node: node,
             function_mutation_pool: pools.0,
             number_mutation_pool: pools.1,
@@ -91,22 +102,27 @@ impl<'a> NodeModifier<'a> {
     }
 
     pub fn mutate_node(&mut self) {
-        match self.picked_node.handler {
-            NodeHandler::Number { number } => {
-                self.picked_node.handler = NodeHandler::Number {
-                    number: (self.number_mutation_pool
-                        [random_range(0..self.number_mutation_pool.len())])(
-                        number
-                    ),
-                };
-            }
-            NodeHandler::Function { function } => {
-                self.picked_node.handler = NodeHandler::Function {
-                    function: self.function_mutation_pool
-                        [random_range(0..self.function_mutation_pool.len())],
+        if random_range(0..TYPE_CHANGE_PROBABILITY) == TYPE_CHANGE_PROBABILITY - 1 {
+        } else {
+            match self.picked_node.handler {
+                NodeHandler::Number { number } => {
+                    self.picked_node.handler = NodeHandler::Number {
+                        number: (self.number_mutation_pool
+                            [random_range(0..self.number_mutation_pool.len())])(
+                            number
+                        ),
+                    };
                 }
+                NodeHandler::Function { function } => {
+                    let selected_mutation = &self.function_mutation_pool
+                        [random_range(0..self.function_mutation_pool.len())];
+                    self.picked_node.max_children_count = selected_mutation.1;
+                    self.picked_node.handler = NodeHandler::Function {
+                        function: selected_mutation.0,
+                    }
+                }
+                _ => {}
             }
-            _ => {}
         }
     }
 }