@@ -94,26 +94,25 @@ new_sol = solve(new_prob, Tsit5())
9494
9595""" 
9696function  change_of_variables (
97-     sys:: System , iv, forward_subs, backward_subs;
98-     simplify= true , t0= missing , isSDE= false 
97+          sys:: System , iv, forward_subs, backward_subs;
98+          simplify  =   true , t0  =   missing , isSDE  =   false 
9999)
100100    t =  iv
101101
102102    old_vars =  first .(backward_subs)
103103    new_vars =  last .(forward_subs)
104-      
104+ 
105105    #  use: f = Y(t, X)
106106    #  use: dY = (∂f/∂t + μ∂f/∂x + (1/2)*σ^2*∂2f/∂x2)dt + σ∂f/∂xdW
107107    old_eqs =  equations (sys)
108108    neqs =  get_noise_eqs (sys)
109109    brownvars =  brownians (sys)
110-     
111-     
110+ 
112111    if  neqs ===  nothing  &&  length (brownvars) ===  0 
113112        neqs =  ones (1 , length (old_eqs))
114113    elseif  neqs != =  nothing 
115114        isSDE =  true 
116-         neqs =  [neqs[i,:] for  i in  1 : size (neqs,1 )]
115+         neqs =  [neqs[i,  :] for  i in  1 : size (neqs,  1 )]
117116
118117        brownvars =  map ([Symbol (:B , :_ , i) for  i in  1 : length (neqs[1 ])]) do  name
119118            unwrap (only (@brownians  $ name))
@@ -135,9 +134,10 @@ function change_of_variables(
135134    end 
136135
137136    #  df/dt = ∂f/∂x dx/dt + ∂f/∂t
138-     dfdt =  Symbolics. derivative ( first .(forward_subs), t )
139-     ∂f∂x =  [Symbolics. derivative ( first (f_sub), old_var ) for  (f_sub, old_var) in  zip (forward_subs, old_vars)]
140-     ∂2f∂x2 =  Symbolics. derivative .( ∂f∂x, old_vars )
137+     dfdt =  Symbolics. derivative (first .(forward_subs), t)
138+     ∂f∂x =  [Symbolics. derivative (first (f_sub), old_var)
139+             for  (f_sub, old_var) in  zip (forward_subs, old_vars)]
140+     ∂2f∂x2 =  Symbolics. derivative .(∂f∂x, old_vars)
141141    new_eqs =  Equation[]
142142
143143    for  (new_var, ex, first, second) in  zip (new_vars, dfdt, ∂f∂x, ∂2f∂x2)
@@ -154,7 +154,7 @@ function change_of_variables(
154154        ex =  substitute (ex, Dict (forward_subs))
155155        ex =  substitute (ex, Dict (backward_subs))
156156        if  simplify
157-             ex =  Symbolics. simplify (ex, expand= true )
157+             ex =  Symbolics. simplify (ex, expand  =   true )
158158        end 
159159        push! (new_eqs, Differential (t)(new_var) ~  ex)
160160    end 
@@ -174,10 +174,11 @@ function change_of_variables(
174174        end 
175175    end 
176176
177-     @named  new_sys =  System (vcat (new_eqs, first .(backward_subs) .~  last .(backward_subs)), t;
178-             defaults= new_defs,
179-             observed= observed (sys)
180-             )
177+     @named  new_sys =  System (
178+         vcat (new_eqs, first .(backward_subs) .~  last .(backward_subs)), t;
179+         defaults =  new_defs,
180+         observed =  observed (sys)
181+     )
181182    if  simplify
182183        return  mtkcompile (new_sys)
183184    end 
@@ -570,7 +571,8 @@ All accumulation variables have a default of zero.
570571function  add_accumulations (sys:: System , vars:: Vector{<:Pair} )
571572    eqs =  get_eqs (sys)
572573    avars =  map (first, vars)
573-     if  (ints =  intersect (avars, unknowns (sys)); ! isempty (ints))
574+     ints =  intersect (avars, unknowns (sys))
575+     if  ! isempty (ints)
574576        error (" $ints  already exist in the system!" 
575577    end 
576578    D =  Differential (get_iv (sys))
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