Note BASIC and FORTRAN (and calculus itself) use = instead of

Find formulas for the outputs $f_1(t)$ and $f_2(t)$ which come from the input $t$:

(1) inside = input * 3

output = inside + 3

(2) inside $\leftarrow$ input + 6

output $\leftarrow$ inside * 3

Note BASIC and FORTRAN (and calculus itself) use = instead of $\leftarrow$. But the symbol $\leftarrow$ or := is in some ways better. The instruction $t\leftarrow t+6$ produces a new $t$ equal to the old $t$ plus six. The equation $t=t+6$ is not intended.

Gilbert Strang, Calculus, 3rd edition (Wellesley-Cambridge Press; MIT OpenCourseWare RES.18-001) · §1.1 Velocity and Distance, #48