(
n1 | u1 n2 | u2 --
n3 | u3 )
Subtract
n2 | u2 from
n1 | u1, giving the
difference
n3 | u3.
Testing:
T{ 0 5 - -> -5 }T
T{ 5 0 - -> 5 }T
T{ 0 -5 - -> 5 }T
T{ -5 0 - -> -5 }T
T{ 1 2 - -> -1 }T
T{ 1 -2 - -> 3 }T
T{ -1 2 - -> -3 }T
T{ -1 -2 - -> 1 }T
T{ 0 1 - -> -1 }T
T{ MID-UINT+1 1 - -> MID-UINT }T