1. The problem is to simplify or understand the expression $x - y + a1$. 2. This expression consists of three terms: $x$, $-y$, and $a1$. 3. Since there are no like terms to combine (assuming $a1$ is a single variable or constant), the expression is already simplified. 4. The expression $x - y + a1$ means you take $x$, subtract $y$, and then add $a1$. 5. Without additional information or values for $x$, $y$, and $a1$, this is the simplest form. Final answer: $x - y + a1$