Properties of the rank of linear algebraic matrix If a matrix has a non-zero r-order subformula, and all R + 1-order subformulas containing this r-order subformula are zero, then the rank of the matrix is R. how to prove its correctness or tell me how to deduce from the definition of matrix rank

Properties of the rank of linear algebraic matrix If a matrix has a non-zero r-order subformula, and all R + 1-order subformulas containing this r-order subformula are zero, then the rank of the matrix is R. how to prove its correctness or tell me how to deduce from the definition of matrix rank

This is a theorem. Please refer to the proof of this theorem