fix tabulation and gaps in expression.rb

lib/ruby_algebra/expression.rb

@@ -69,6 +69,7 @@ module RubyAlgebra
     def type
       :sub
     end
+
     def diff(v)
       Subtraction.new(@lhs.diff(v), @rhs.diff(v))
     end
@@ -114,6 +115,7 @@ module RubyAlgebra
     def op_assoc_type
       :left
     end
+
     def diff(v)
       u_prime = @lhs.diff(v)
       v_prime = @rhs.diff(v)
@@ -176,6 +178,7 @@ module RubyAlgebra
     def op_assoc_type
       :right
     end
+
     def diff(v)
       unless @exponent.is_a?(Constant)
         raise NotImplementedError, "Дифференцирование степени с неконстантным показателем не реализовано"
@@ -244,6 +247,7 @@ module RubyAlgebra
     def single_letter?
       @is_single_letter
     end
+
     def diff(v)
       @symbol == v ? Constant.new(1) : Constant.new(0)
     end