if length of a = 0 that means b is not present in a so we return false
if ( a . length ( ) == 0 ) return false ; if ( a . charAt ( 0 ) == b . charAt ( 0 ) ) return checkSequence ( a . substring ( 1 ) , b . substring ( 1 ) ) ; else return checkSequence ( a . substring ( 1 ) , b ) ; }