HP49-HP50 Lists of combination

[Gil]

Suppose that I have 7 variables or objects , x1... x7.

Suppose that I fix x1 in function of 4 other variables,
say x1=a2x2+ a3x3+ a4x4 + a5x5.

How could I get all the groups of 4 variables
(6!/(4!*2!) = 5*6/2 = 15 possibilities, for example in a big list like, not including x1:

{{x2, x3, x4, x5}
{x2, x3, x4, x6}
{x2, x3, x4, x7}

x2, x3, x5, x6}
x2, x3, x5, x7}
x2, x3, x6, x7}

x2, x4, x5, x6}
x2, x4, x5, x7}
x2, x4, x6, x7}

x2, x5, x6, x7}

x3, x4, x5, x6}
x3, x4, x5, x7}
x3, x4, x6, x7}

x3, x5, x6, x7}

x4, x5, x6, x7}}

entering two arguments, in this example n=7 and m=4 in HP50G?

Unfortunately I get stuck to that problem. I think that I should use a recursive program, as n and m are variable parameters.

Thanks in advance for your help.

Gil