91) and (2.92):
$$
m(\mathrm{N}) = \frac{1}{2} [m(\pi) + m(\rho)] - a
$$
$$
m(\Delta) = \frac{1}{2} [m(\pi) + m(\rho)] - a^{\prime}
$$
Now, we want to show that the delta is heavier than the nucleon. To do this, we need to show that $m(\Delta) > m(\mathrm{N})$.
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