This challenge is to make up YOUR OWN wordarithmetic challenge.
Each letter represents a digit and where the same letter appears more than once it must represent the same digit each time.
The hard part is to make up some message rather than just using any old letters. Send in your wordarithmetic challenge, together with at least one solution to it.
Another challenge is to discover if the puzzle has just one solution or many. Here are two easy examples; they are just addition sums and you may be more inventive and make up subtractions, multiplications or divisions:

N 
R 
I 
C 
H 
+ 
S 
T 
A 
R 
S 

M 
A 
T 
H 
S 



M 
A 
T 
H 
+ 
E 
M 
A 
T 

I 
C 
A 
L 

Lastly, can you prove that

N 
R 
I 
C 
H 
+ 
M 
A 
T 
H 
S 

S 
T 
A 
R 
S 
cannot be made to work?