12Lxx Connections with logic

• 12L05 Decidability [See also 03B25]
• 12L10 Ultraproducts [See also 03C20]
• 12L12 Model theory [See also 03C60]
• 12L15 Nonstandard arithmetic [See also 03H15]
• 12L99 None of the above, but in this section