pointerType ~ null

3.9: adda/syntax/type/pointerType ~ null:
. the syntax:
x.pointerType~null
means a pointer type that excludes null values .
. that could be slightly confusing
since this(~) is a truth or set operation,
it could apply to the object instead of its type;
but since (var~null) trivially reduced to var,
it will never be used,
so we can assume it applies to the type .