books active form is not a plural
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# Plural
# Math formula
# forbidding formula
# Euler's formula
# prayer formula
# tashahhud formula
# Teaching formula
# perfect formula
# finite plural form
# An individual in the plural form and other poems
# formula unit
# Rydberg formula
# ambiguous ruling formula
# Atom formula
# structural formula
# chemical formula
# syntax formula
# normal formula game
# Bacchus Nour formula
# Path integration formula
