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% replaces any number of letters (la% - lake, lamp)_ replaces one letter (ca_ - car, cat)

Crossword clues for Einstein's "m":

MASS: The "m" in Einstein's famous equation
MASS: M, to Einstein
MASS: Einstein's "m"
MASS: M, in Einstein's equation
MASS: The "m" in Einstein's E = mc^2
MASS: The "m" in Einstein's equation