You are free to break the lines when writing R code, but be careful to R functions when there are operators `+`

or `-`

in your expression to return:

```
f1 = function() {
1 + 1
}
f1() # of course 2
f2 = function() {
1
+ 1
}
f2() # returns 1
f3 = function() {
return(1
+ 1)
}
f3() # 2; use return() if you want break lines, or
f4 = function() {
1 +
1
}
f4() # 2; don't put '+' in the beginning, as '+1==1'
```

These examples are quite simple, but sometimes you will forget this rule, e.g.:

```
testMat = function(len = 50, digits = c(3, 5, 7, 9, 11, 13, 15, 17, 19)) {
n = length(digits)
matrix(1:0, 2 * len, n)
+ matrix(10^digits, 2 * len, n, byrow = TRUE)
}
```

Can you find out the error in the above function without reading my hints beforehand?