fixup! fix: remove usages of occursin for searching expressions

Author: AayushSabharwal

src/utils.jl

@@ -148,7 +148,7 @@ function check_variables(dvs, iv)
     for dv in dvs
         isequal(iv, dv) &&
             throw(ArgumentError("Independent variable $iv not allowed in dependent variables."))
-        (is_delay_var(iv, dv) || SU.query!(isequal(iv), dv)) ||
+        (is_delay_var(iv, dv) || SU.query(isequal(iv), dv)) ||
             throw(ArgumentError("Variable $dv is not a function of independent variable $iv."))
     end
 end