Multiply $\frac{1}{2}$ and $-1$ to get $-\frac{1}{2}$.
$$sort(\frac{20}{21},\frac{4}{5}-\frac{1}{2})$$
Least common multiple of $5$ and $2$ is $10$. Convert $\frac{4}{5}$ and $\frac{1}{2}$ to fractions with denominator $10$.
$$sort(\frac{20}{21},\frac{8}{10}-\frac{5}{10})$$
Since $\frac{8}{10}$ and $\frac{5}{10}$ have the same denominator, subtract them by subtracting their numerators.
$$sort(\frac{20}{21},\frac{8-5}{10})$$
Subtract $5$ from $8$ to get $3$.
$$sort(\frac{20}{21},\frac{3}{10})$$
Least common denominator of the numbers in the list $\frac{20}{21},\frac{3}{10}$ is $210$. Convert numbers in the list to fractions with denominator $210$.
$$\frac{200}{210},\frac{63}{210}$$
To sort the list, start from a single element $\frac{200}{210}$.
$$\frac{200}{210}$$
Insert $\frac{63}{210}$ to the appropriate location in the new list.
$$\frac{63}{210},\frac{200}{210}$$
Replace the obtained fractions with the initial values.
