Groovy's powerful collection methods

Recently I just realize Groovy provides some handy methods for collections.

Permutations

	[1,2,3].permutations()
	//[[1, 2, 3], [3, 2, 1], [2, 1, 3], [3, 1, 2], [1, 3, 2], [2, 3, 1]]

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Combinations

	letters = ['a', 'b', 'c']
	numbers = [1, 2, 3]
	combos = [letters, numbers].combinations()
	//[[a, 1], [b, 1], [c, 1], [a, 2], [b, 2], [c, 2], [a, 3], [b, 3], [c, 3]]

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Subsequences

	[1,2,3].subsequences()
	//===> [[1], [1, 2, 3], [2], [2, 3], [1, 2], [3], [1, 3]]

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Intersect

	[1,2,3,4].intersect([2,4])
	//===> [2, 4]

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