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## Main Question or Discussion Point

A theorem from number theory states that, if a and b are nonzero integers, then there exists a smallest positive linear combination of a and b.

This is my proof:

Let S be a set such that S = {w[itex]\in[/itex]Natural numbers : w=am+bn} , where a and b are positive integers, m and n are any integers, and w is by definition a linear combination of a and b.

Suppose S is nonempty. Then S is a subset of the natural numbers. Then by the Well Ordering Principle, S has a smallest (positive) element. Thus there exists a smallest positive linear combination of a and b.

Is this correct? Or am I missing something? My professor said that fastest way to prove this is by contradiction, but it seems to me that just directly proving by the well ordering principle is faster?

This is my proof:

Let S be a set such that S = {w[itex]\in[/itex]Natural numbers : w=am+bn} , where a and b are positive integers, m and n are any integers, and w is by definition a linear combination of a and b.

Suppose S is nonempty. Then S is a subset of the natural numbers. Then by the Well Ordering Principle, S has a smallest (positive) element. Thus there exists a smallest positive linear combination of a and b.

Is this correct? Or am I missing something? My professor said that fastest way to prove this is by contradiction, but it seems to me that just directly proving by the well ordering principle is faster?