diff --git a/arc.bqn b/arc.bqn
index ca8b193..1537297 100755
--- a/arc.bqn
+++ b/arc.bqn
@@ -7,15 +7,16 @@
 
 opts←{
   a←•args
-  •Show a
   chars ⇐{0=≠𝕩?" λ$⊕⭍#/\-|+<>^v";⊑𝕩}(»(<"--chars")⊸⍷)⊸/a
   fchars⇐{0=≠𝕩?" λ$⊕⭍#/\-|+<>^v";⊑𝕩}(»(<"--fchars")⊸⍷)⊸/a
-  levels⇐{0=≠𝕩?"levels";⊑𝕩}(»(<"--levels")⊸⍷)⊸/a
+  l←{0=≠𝕩?"levels";⊑𝕩}(»(<"--levels")⊸⍷)⊸/a
+  levels⇐{0=≠𝕩?l;⊑𝕩}(»(<"-l")⊸⍷)⊸/a
+  n⇐{0=≠𝕩?1;1⌊⊑𝕩}•BQN¨⎊{𝕊: •Out "Invalid starting level number" ⋄ •Exit 1}(»(<"-s")⊸⍷)⊸/a
 }
 
+g←Game⎊{𝕊: •Out •CurrentError @ ⋄ •Exit 1} opts.n‿opts.levels‿opts.chars‿opts.fchars‿⟨ansi.defaultB,ansi.yellow,ansi.cyan,ansi.red⟩
 ansi.InitTerm @
 clear←""
-g←Game opts.levels‿opts.chars‿opts.fchars‿⟨ansi.defaultB,ansi.yellow,ansi.cyan,ansi.red⟩
 {𝕤 # Loop until the user wins
   •Out clear∾ansi.cursor.origin
   clear↩""
diff --git a/logic.bqn b/logic.bqn
index 98573e7..fca1fab 100644
--- a/logic.bqn
+++ b/logic.bqn
@@ -5,7 +5,8 @@
 ⟨FindIdx,SplitOnEmpty⟩←•Import "utils.bqn"
 
 Game⇐{ # The Game function creates a game object
-  𝕊 levelPath‿dchars‿chars‿colors: # from parameters:
+  𝕊 n‿levelPath‿dchars‿chars‿colors: # from parameters:
+  # n: starting level
   # levelPath: the path of the file containing the levels
   # dchars: the characters to use for drawing
   # chars: the characters that are used in the level representation
@@ -125,8 +126,14 @@ Game⇐{ # The Game function creates a game object
   # -------------------------------------------------------------------------------
 
   moves⇐⟨0‿0⟩ # list of moves, each move is a direction, we start without moving
-  currentLevel⇐0
+  currentLevel⇐n-1
+  "Invalid number of fchars" ! 15=≠chars
+  "Invalid number of chars"  ! 15=≠dchars
+  "The level file contains illegal characters" ! ∧´chars∊˜∾´•Flines levelPath
   levels←Ascii2Matrix¨>¨SplitOnEmpty•FLines levelPath # Load file containing levels
+  "Some levels don't contain any player" ! ¬∨´0=≠¨{player FindIdx ⊑¨𝕩}¨levels
+  "Some levels don't contain any machine" ! ¬∨´0=≠¨{machine FindIdx ⊑¨𝕩}¨levels
+  "The starting level is higher than the number of levels" !  currentLevel<≠levels
   Next⇐{moves↩moves∾<𝕩}
   Undo⇐{𝕊:moves↩(-1<≠)⊸↓moves}
   Draw⇐{𝕊:•Out¨ (currentLevel⊑levels) DrawLevel moves}