VTI Unit 1, Pt A, L2

Any mathematical expression which contains neither a relation symbol nor a placeholder symbol. For example, 2(5 - 1) is a closed phrase

any mathematical expression which contains a placeholder symbol, but does not contain a relation symbol. For example, 6 + [3 - n] is an open phrase

Any mathematical expression which contains a relation symbol, but does not contain a placeholder symbol. For example, 7(4 - 2) = 13 is a closed sentence.

Any mathematical expression which contains both a relation symbol and a placeholder symbol. For example, 9 + 2[n - 4] > 12 is an open sentence.