I have a homework with the problem set like the following:
When a B-spline is evaluated at one of its knots it can be simplified according to the formula
$B(t_i | t_j,...,t_{j+1+p}) = B(t_i | t_j,...,t_{i-1},t_{i+1},t_{j+1+p})$
What does the vertical bar means here? I can see that the right hand side skips $t_i$.