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diff --git a/server/game/utils.lisp b/server/game/utils.lisp
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+(in-package :remote-snake-server-game)
+
+;;; Return true when doing a legal move (ex: snake can goto left when it is in the right direction)
+(defun legal-move (active-dir dir)
+  (or
+   (eq active-dir dir) ; Goto same direction
+   (and (or (eq dir :up) (eq dir :down)) ; Got up or down only if the snake is on the left or right direction
+        (or (eq active-dir :left) (eq active-dir :right)))
+   (and (or (eq dir :left) (eq dir :right)) ; Goto left or right only if the snake is on the up or down direction
+        (or (eq active-dir :up) (eq active-dir :down)))))
+
+;;; Grow snake of grow-size amount (snake is growing by the tail)
+(defun grow-snake (snake grow-size)
+  (let* ((old-size (length snake))
+         (new-size (+ old-size grow-size))
+         (tail (nth (- old-size 1) snake))
+         (new-tail (make-list grow-size :initial-element tail)))
+    (append snake new-tail)))
+
+;;; Function to compare two list of two elements
+(defun equal-coord (c1 c2)
+  (let ((x1 (car c1))
+        (x2 (car c2))
+        (y1 (car (cdr c1)))
+        (y2 (car (cdr c2))))
+    (and (eql x1 x2) (eql y1 y2))))
+
+;; Remove a coord from a list of coord (usefull when snake is eating a food)
+(defun remove-coord (l c)
+  (if (eql l '()) l ; Terminal condition
+    (let ((head (first l)))
+      (if (equal-coord head c)
+          (remove-coord (cdr l) c)
+        (append `(,head) (remove-coord (cdr l) c))))))