Bug: type-constraint not applied

[timoniq]

Expected and real behaviour:

query as_boolean(prime, x) = @false must produce only natural solutions for x due to prime signature ?prime(natural).

but it also produces integer results.

How to reproduce:

as_boolean(prime, x) = @false
-- to fix 'x' can be predefined
x ~ natural, as_boolean(prime, x) = @false

System info

laurelang: dev

OS: unix