give a < > b
unless
    [ , b , c , < , > , ]
    , a a !! , a c !! , a < !! , a ] !!
    , a b b , a b ] ;

give < c b
unless
    [ , b , c , < , > , ]
    , a a !! , a b !! , a c !! , a ] !!
    , a < c , a < > ;

give [
unless
    a , b , c , < , > , ]
    , [ a !! , [ b !! , [ c !! , [ ] !!
    , [ < c ;

give c >
unless
    [ , a , b , c , < , ]
    , > ] !!
    , > b b , > b ] ;

give ]
unless
    [ , a , b , c , < , ]
    , > b !! ;

give c b
unless
    [ , a , c , < , > , ]
    , b b !! , b > !! , b ] !!
    , b c b , b c c , b c > , b c ] ;

give [ a
unless
    a , b , c , < , > , ]
    , [ a !! , [ b !! , [ < !! , [ ] !!
    , [ c b , [ c c  ;

give a a
unless
    [ , b , c , < , > , ]
    , a a !! , a b !! , a < !! , a ] !!
    , a c c , a c b ;

have [ a b ] ;