$1-$ Simplify the following Boolean function:

$F=a^{\text{'}}{b}^{\text{'}}{c}^{\text{'}}{d}^{\text{'}}+a^{\text{'}}{b}^{\text{'}}c{d}^{\text{'}}+a{b}^{\text{'}}{c}^{\text{'}}{d}^{\text{'}}+a{b}^{\text{'}}c{d}^{\text{'}}+a^{\text{'}}b{c}^{\text{'}}d+a^{\text{'}}bcd+ab{c}^{\text{'}}d+$abcd