# Inconsistency in function return value

```
┌────────────────────────────────────────────────────────────────────┐
│ SageMath version 9.0, Release Date: 2020-01-01 │
│ Using Python 3.7.3. Type "help()" for help. │
└────────────────────────────────────────────────────────────────────┘
sage: p = lambda x: (x - 1) / 2
sage: p(11)
5
sage: is_prime(5)
True
sage: is_prime(p(11))
False
sage:
```

In above example, `is_prime`

function returns `true`

when called like `is_prime(5)`

. However, when I give it `p(11)`

, which returns 5, as an argument, function returns `false`

.

What is the reason for this behaviour, and how can I fix it?