subrange-check.dfy(5,30): Error: value of expression (of type 'object?') is not known to be an instance of type 'object', because it might be null
 Asserted expression: o is object
subrange-check.dfy(6,28): Error: value does not satisfy the subset constraints of 'T -> U' (possible cause: it may be partial or have read effects)
 Asserted expression: p is T -> U
subrange-check.dfy(7,31): Error: value does not satisfy the subset constraints of 'T --> U' (possible cause: it may have read effects)
 Asserted expression: r is T --> U
subrange-check.dfy(8,23): Error: value does not satisfy the subset constraints of 'nat'
 Asserted expression: i is nat

Dafny program verifier finished with 0 verified, 4 errors
