Can you obtain a given integer as a sum of two elements from a given list of integers?

Assignment

Write a function combisum to which two arguments must be passed: a list of integers and an integer. The function must return a Boolean value as result, indicating whether the given integer may be obtained as the sum of two numbers from the data list.

Example

>>> combisum([1, 2, 3, 4, 5, 6], 10)
True
>>> combisum([3, 9, -4, 2, 5], -3)
False
>>> combisum([-3, 7, 9, 20, 1], 17)
True