Unexpected "=" in ifelse loops

I want to create a new column 'fgroup' based on the various combinations of values in three other columns: 'GVT', 'FOTH' and 'UNK', all three columns having either values 0 or 1. I have made this script using MUTATE.

sysrev$fclass <- mutate(ifelse(sysrev$GVT=1 & sysrev$FOTH=0 & sysrev$UNK=0, sysrev$fgroup=1),
                        ifelse(sysrev$GVT=1 & sysrev$FOTH=1 & sysrev$UNK=0, sysrev$fgroup=2),
                        ifelse(sysrev$GVT=0 & sysrev$FOTH=1, sysrev$fgroup=3),
                        ifelse(sysrev$GVT=0 & sysrev$FOTH=0 & sysrev$UNK=1, sysrev$fgroup=4))

However, it returns the error message:

Error: unexpected '=' in "                        ifelse(sysrev$GVT="

This is probably easy but I need some advice...