Transitive closures of relations follow the well-known syntax of regular expressions where patterns to be repeated are enclosed in parentheses with a quantifier appended. The possible quantifiers are:

• + : 1-to-n repetitions.
• * : 0-to-n repetitions.
• ? : 0-to-1 repetitions.
• {n} : exactly n repetitions,
• {n,m} : n-to-m repetitions.
• {n,} : least n repetitions.