Error (10500): VHDL syntax error at mux5to1.vhd(15) near text "IN"; expecting an identifier ("in" is a reserved keyword), or a string literal what is the problem?

SIGNALs do not have IN/OUT designations. It should be:

SIGNAL m0,m1,m2: STD_LOGIC_VECTOR(2 DOWNTO 0);

The error is pushed down to line 15 because that's the first line after this error.

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