1 <span class="re8">\begin</span><span class="sy0">{</span><span class="re9"><span class="re7">align*</span></span><span class="sy0">}</span> <span class="co1">% *: sem numerar</span>
2 a = b <span class="sy0">&</span><span class="re12">\iff</span> a^2 = ab <span class="sy0">\\</span>
3 <span class="sy0">&</span><span class="re12">\iff</span> a^2 - b^2 = ab - b^2 <span class="sy0">\\</span>
4 <span class="sy0">&</span><span class="re12">\iff</span> (a + b)(a - b) = b(a - b) <span class="sy0">\\</span>
5 <span class="sy0">&</span><span class="re12">\iff</span> a + b = b <span class="sy0">\\</span>
6 <span class="sy0">&</span><span class="re12">\iff</span> 2b = b <span class="sy0">\\</span>
7 <span class="sy0">&</span><span class="re12">\iff</span> 2 = 1
8 <span class="re8">\end</span><span class="sy0">{</span><span class="re9"><span class="re7">align*</span></span><span class="sy0">}</span>