ex-4: fix some typos

ex-4/lib.c

@@ -56,6 +56,7 @@ double exp1d (double x, double p_max)
   return x/(a*B) - x*C/(a*A*pow(B, 2));
   }
 
+
 //
 // Second derivative of the expected function.
 //

ex-4/lib.h

@@ -24,7 +24,7 @@ struct parameters
 
 // Minimization wrapper.
 //
-double chi2(double p_max, void* params);
+double chi2 (double p_max, void* params);
 
 // Expected function.
 //

ex-4/main.c

@@ -116,7 +116,7 @@ int main(int argc, char **argv) {
     if (go == 1) printf("\n%.5f", histo[i].sum);
   };
   
-  /* Compare the histigram with the expected function:
+  /* Compare the histogram with the expected function:
    *
    *   x * log(p_max/x)/arctan(sqrt(p_max^2/x^2 - 1))
    *