In order for <em>F</em> to be conservative, there must be a scalar function <em>f</em> such that the gradient of <em>f</em> is equal to <em>F</em>. This means
Integrate both sides of the first equation with respect to <em>x</em> :
Differentiate both sides with respect to <em>y</em> :
But we assume <em>g</em> is a function of <em>y</em>, which means its derivative can't possibly contain <em>x</em>, so there is no scalar function <em>f</em> whose gradient is <em>F</em>. Therefore <em>F</em> is not conservative.