LaTex math mode coding

Question

This is my code, in begin{align*} why am I getting an error saying I'm missing a $?
begin{document}
%%
begin{proof*}
begin{align*}

1.; & (p land q rightarrow r, u rightarrow lnot r, u land q) &&aside{Premise}
2.; & p land q rightarrow r   &&aside{Premise} 
3.; & equiv u rightarrow lnot r     &&aside{Premise} 
4.; & equiv u land q                 &&aside{Premise} 
5.; & equiv u                         &&aside{Specialization:3} 
6.; & equiv land r                   &&aside{Modus Pones:2,4} 
7.; & equiv lnot (p land q)         &&aside{Modus Tollens:1,5} 
8.; & equiv lnot p lor lnot q      &&aside{De Morgan's: ^} 
9.; & equiv q                         &&aside{Specialization:3}
10.; & equiv lnot lnot q             &&aside{Double Negation:8}
11.; & equiv lnot p                   &&aside{Elimination:7,9}
                    
end{align*}
end{proof*}

%%
end{document}

Zarko · Answer

Welcome to TeX.SE!
To long for a comment ...
Since you not provide MWE, the following is based on usual use of the proof environment (see Theorems). In it is considered @Mico comment (removed are blank lines in align environment):
documentclass{article}
usepackage{amsmath,amsthm}
newcommandaside[1]{text{#1}}

begin{document}
    begin{proof} % <---
begin{align*}
    1.quad & (p land q to r, u to lnot r, u land q) 
                        &&aside{Premise}
    2.quad & p land q rightarrow r   &&aside{Premise} 
    3.quad & equiv u rightarrow lnot r     &&aside{Premise} 
    4.quad & equiv u land q                 &&aside{Premise} 
    5.quad & equiv u                         &&aside{Specialization:3} 
    6.quad & equiv land r                   &&aside{Modus Pones:2,4} 
    7.quad & equiv lnot (p land q)         &&aside{Modus Tollens:1,5} 
    8.quad & equiv lnot p lor lnot q      &&aside{De Morgan's: } 
    9.quad & equiv q                         &&aside{Specialization:3}
    10.quad & equiv lnot lnot q            &&aside{Double Negation:8}
    11.quad & equiv lnot p                  &&aside{Elimination:7,9}
        qedhere
end{align*}%
    end{proof} % <---
end{document}

It gives no errors! Where and how you define ˙proof*`?

Masum · Answer

For some reason, align environment cannot process empty lines. So remove the empty lines and it should compile fine

LaTex math mode coding

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