-- returns a list with elements from all even posistion of the input list
evenpos :: [a] -> [a]
evenpos [] = []
evenpos [a] = []
evenpos [a,b] = [b]
evenpos [a,b,c] = [b]
evenpos [a,b,c,d] = [b,d]
evenpos [a,b,c,d,e] = [b,d]
evenpos [a,b,c,d,e,f] = [b,d,f]