columns.dfy(8,0): Warning: module-level methods are always non-instance, so the 'static' keyword is not allowed here
columns.dfy(9,9): Error: assertion might not hold
columns.dfy(10,11): Error: assertion might not hold
columns.dfy(11,11): Error: assertion might not hold

Dafny program verifier finished with 0 verified, 3 errors
