diff --git a/board.lua b/board.lua
index 0163738..6212d3f 100644
--- a/board.lua
+++ b/board.lua
@@ -99,48 +99,59 @@ function Board.new()
 		end,
 
 		is_valid = function(self)
+			return #self:get_issues() == 0
+		end,
+
+		get_issues = function(self, details)
 			local rows = self:get_rows()
+			local issues = {}
 			for y,row in ipairs(rows) do
 				-- check count
 				if count(row, BLUE) ~= count(row, YELLOW) then
+					add(issues, {"row", "count", row, y})
 					if (debug) printh("uneven count on row "..y)
-					return false
+					if (not details) return issues
 				end
 				-- check identical lines
 				for k,other in ipairs(rows) do
 					if equal(other, row) and other ~= row then
+						add(issues, {"row", "identical", row, y, k})
 						if (debug) printh("equal rows "..k)
-						return false
+						if (not details) return issues
 					end
 				end
 				-- check triples
 				if self:count_consecutives(row) > 2 then
+					add(issues, {"row", "triples", row, y})
 					if (debug) printh("triples")
-					return false
+					if (not details) return issues
 				end
 			end
 
 			local cols = self:get_cols()
-			for col in all(cols) do
+			for x,col in ipairs(cols) do
 				-- check count
 				if count(col, BLUE) ~= count(col, YELLOW) then
+					add(issues, {"col", "count", col, x})
 					if (debug) printh("uneven count")
-					return false
+					if (not details) return issues
 				end
 				-- check identical lines
-				for other in all(cols) do
+				for k,other in ipairs(cols) do
 					if equal(other, col) and other ~= col then
+						add(issues, {"col", "identical", col, x, k})
 						if (debug) printh("equal cols")
-						return false
+						if (not details) return issues
 					end
 				end
 				-- check triples
 				if self:count_consecutives(col) > 2 then
+					add(issues, {"col", "triples", col, x})
 					if (debug) printh("triples")
-					return false
+					if (not details) return issues
 				end
 			end
-			return true
+			return issues
 		end,
 
 		count_consecutives = function(self, line)
diff --git a/coroutines.lua b/coroutines.lua
index 749f207..2ff1441 100644
--- a/coroutines.lua
+++ b/coroutines.lua
@@ -1,14 +1,12 @@
 local coroutines={}
 
--- starts a coroutine and returns its key
-function startcoroutine(fn, key)
+-- starts a coroutine and saves it for future reference
+function startcoroutine(fn)
+	assert(tostr(fn) == "[thread]") -- make sure that fn is a coroutine, the return value of cocreate()
 	add(coroutines, fn)
 end
 
-function stepcoroutine(fn)
-  coresume(fn)
-end
-
+-- stops the the coroutine
 function stopcoroutine(fn)
 	del(coroutines, fn)
 end
@@ -23,10 +21,12 @@ function _coresolve()
   end
 end
 
+-- to be used inside a coroutine
 function wait(seconds)
   wait_frames(seconds*60)
 end
 
+-- to be used inside a coroutine
 function wait_frames(frames)
   for i=1,frames do
     yield()
diff --git a/states/game.lua b/states/game.lua
index 868e694..fcf7baf 100644
--- a/states/game.lua
+++ b/states/game.lua
@@ -2,6 +2,15 @@ function state_game()
 
 	local board
 	local selected_id = 1
+	local timer_clue = 0
+
+	local function show_clues()
+		-- local result = board:is_valid()
+		-- if result ~= true and result ~= false then
+		-- 	local rule,what,where = unpack(result)
+		-- 	--printh("Rule: " .. rule .. " " .. what .. " " .. where[1].. " " .. where[2])
+		-- end
+	end
 
 	local function draw_selected_tile()
 		local x, y = board:draw_coords(selected_id)
@@ -17,6 +26,10 @@ function state_game()
 		board:lock_tiles()
 	end
 
+	local function _leave()
+		-- stopcoroutine(show_clues)
+	end
+
 	local function _draw()
 		cls()
 		board:draw()
@@ -24,6 +37,10 @@ function state_game()
 	end
 
 	local function _update()
+		timer_clue += 1
+		if timer_clue % 120 == 0 then
+			show_clues()
+		end
 		local size = board:get_size()
 		local x, y = board:idx_xy(selected_id)
 		if btnp(UP) then
@@ -51,5 +68,6 @@ function state_game()
 		_enter = _enter,
 		_update = _update,
 		_draw = _draw,
+		_leave = _leave
 	}
 end
\ No newline at end of file