ngn pointed this out before. i discovered myself the other day. k4 parse:
p:-5! /parse
a:"{x+y}[1;]"
b:"{x+y}[1;::]"
`p@a
({x+y};1;::)
`p@b
({x+y};1;::)
(`p@a)~`p@b
1b
^*|`p@a
0b
^*|`p@b
1b
p:-5! /parse
a:"{x+y}[1;]"
b:"{x+y}[1;::]"
`p@a
({x+y};1;::)
`p@b
({x+y};1;::)
(`p@a)~`p@b
1b
^*|`p@a
0b
^*|`p@b
1b
