Add citation utility class and improve grid naming

- Rename layout-2col grid area 'footer' to 'buffer' for clarity
- Add .cite utility class for bottom-left citations
- Include citation examples in both demo presentations
- Document citation usage in README

4 files changed, 31 insertions, 7 deletions

diff --git a/README b/README
index 8f69673..9f18db3 100644
--- a/README
+++ b/README
@@ -54,6 +54,16 @@ Text content
 </div>
 ```
 
+### `cite` - Citation/Attribution
+```markdown
+---
+### Slide Title
+
+Your content here
+
+<div class="cite">[Author et al., Year]</div>
+```
+
 ### Default - Single Column
 ```markdown
 ---
diff --git a/acarp.css b/acarp.css
index 6395e52..98363d7 100644
--- a/acarp.css
+++ b/acarp.css
@@ -310,6 +310,16 @@ section p > img:only-child {
   margin: 0 auto;
 }
 
+/* Citation utility - bottom left corner */
+.cite {
+  position: absolute;
+  bottom: 30px;
+  left: var(--padding);
+  font-size: 0.7em;
+  color: #888888;
+  opacity: 0.9;
+}
+
 /* ============================================================================
    LAYOUT: title
    
@@ -377,7 +387,7 @@ section.layout-2col {
   grid-template-areas:
     "title title"
     "left right"
-    "footer footer";
+    "buffer buffer";
   gap: 2em;
   padding: 0;
   height: 100%;
diff --git a/demo-beamer.md b/demo-beamer.md
index 9a5fec9..db2efa7 100644
--- a/demo-beamer.md
+++ b/demo-beamer.md
@@ -62,16 +62,18 @@ A minimal, grid-based setup for Marp presentations:
 
 The TF-IDF model for term weighting:
 
-$$\text{tf-idf}(t, d, D) = \text{tf}(t, d) \times \text{idf}(t, D)$$
+$\text{tf-idf}(t, d, D) = \text{tf}(t, d) \times \text{idf}(t, D)$
 
 Where term frequency is:
-$$\text{tf}(t, d) = \frac{f_{t,d}}{\sum_{t'\in d} f_{t',d}}$$
+$\text{tf}(t, d) = \frac{f_{t,d}}{\sum_{t'\in d} f_{t',d}}$
 
 And inverse document frequency:
-$$\text{idf}(t, D) = \log \frac{|D|}{|\{d \in D : t \in d\}|}$$
+$\text{idf}(t, D) = \log \frac{|D|}{|\{d \in D : t \in d\}|}$
 
 The 4:3 format provides better vertical space for multi-line equations.
 
+<div class="cite">[Sparck Jones, 1972]</div>
+
 
 ---
 ### Code Examples
diff --git a/demo-standard.md b/demo-standard.md
index 20d887f..1e1ea75 100644
--- a/demo-standard.md
+++ b/demo-standard.md
@@ -72,13 +72,15 @@ A minimal, grid-based setup for Marp presentations:
 
 The TF-IDF model for term weighting:
 
-$$\text{tf-idf}(t, d, D) = \text{tf}(t, d) \times \text{idf}(t, D)$$
+$\text{tf-idf}(t, d, D) = \text{tf}(t, d) \times \text{idf}(t, D)$
 
 Where term frequency is:
-$$\text{tf}(t, d) = \frac{f_{t,d}}{\sum_{t'\in d} f_{t',d}}$$
+$\text{tf}(t, d) = \frac{f_{t,d}}{\sum_{t'\in d} f_{t',d}}$
 
 And inverse document frequency:
-$$\text{idf}(t, D) = \log \frac{|D|}{|\{d \in D : t \in d\}|}$$
+$\text{idf}(t, D) = \log \frac{|D|}{|\{d \in D : t \in d\}|}$
+
+<div class="cite">[Sparck Jones, 1972]</div>
 
 ---